In general there are two flavors of X desktop. The two most famous "heavyweight" desktop projects are GNOME and KDE; these include both a desktop environment and an application development framework. A desktop environment includes a window manager, help browser, file manager, task bar, and so on. A development framework includes any number of libraries to ease application development, perhaps most importantly a GUI toolkit. GNOME and KDE are the desktops with the most support from Linux distribution vendors.

The second flavor of X desktop includes a desktop environment only; no development framework is included. The line between this flavor of desktop and a plain old window manager is a bit blurry; many people would describe Xfce, WindowMaker, and Enlightenment as desktops in this category.

Desktops can be mixed-and-matched; for example, you can run Enlightenment together with GNOME or KDE components; you can run applications developed with the GNOME or KDE development framework under any of the X desktops. One purpose of freedesktop.org is to ensure that this mixing-and-matching remains possible, and promote more of it. Read our Mission Statement for details. The executive summary is that people or organizations developing applications do not need to worry about which desktop their users will select. Applications which work with any desktop are easy to write.

One way to think about the mission of freedesktop.org is this: to ensure that the different development frameworks aren't user-visible.